It is weird that our society frowns upon writers copying/imitating other writers unlike for artists and musicians. I guess the major difference is that unless you are typing on a typewriter or writing by hand, you have a lot of opportunity to go back and fix something before it is presented, while many other types of artists and musicians practice in order to train their hands to be perfect for a one-shot deal.

But non-writing art is given a lot of leeway in terms of covers and imitations, so it's probably many people thinking that writing is easy. Although some of the attitude against fan fiction comes from prominent writers, whereas many popular artists and musicians got their start from imitations and doing covers, and the top artists and musicians seem (at least on the outside) pretty receptive to up and comers/colleagues doing such things as more of a sign of homage than stealing.